案例十一 、使用jQuery动态追加页面数据以及事件委托

我们要执行的任务是页面起初有一部分图片，我们在底下有一个More Photos的链接，点击后，向当前页面后加载一部分图片，再点击该链接，继续加载，直到将我们列出的页面加载完成，此时该链接也消失了。

首先效果图如下：

这个只截取了最底下的一部分页面。在鼠标悬停在图片上时，还会有文字出现，鼠标移出时文字消失。
我们现在要做的就是点击底下的MorePhotos链接时，再加载一部分数据，然后再点击在加载一部分数据，直到数据加载完。
首先body中代码如下：

<div id = "container"><h1> Photo Gallery</h1><div id = "gallery">    <div class = "photo">        <img src = "./images/1.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye ....</div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>    <div class = "photo">        <img src = "./images/2.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye.... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/3.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye.... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>....//若干图片</div> <div class = "link"><a id = "more-photos" href = "1.html"> More Photos &gt;&gt;</a></div> </div>

然后在同一根目录下写几个HTML代码片段，用于加载。

如，我这有一个1.html代码如下

<div class = "photo">        <img src = "./images/1.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>    <div class = "photo">        <img src = "./images/2.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/3.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/4.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/5.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/6.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>

在这个HTML片段中我引入了6个图片。其他的片段如2.html等等都可以仿照上面的这个来写。在定义好了许多个HTML片段后，利用jQuery进行动态追加数据。

首先引入一个jquery库 http://libs.baidu.com/jquery/1.9.0/jquery.js

<script>    $(document).ready(function(){    //首先定义一个变量来记录当前是多少页        var pageNum = 1;        //给链接添加点击事件        $("#more-photos").click(function(event){            event.preventDefault();            var $link = $(this);            //获得当前所点链接的url            var url = $link.attr('href');            //如果该链接的url存在，进行页面追加            if(url){                $.get(url, function(data){                    $("#gallery").append(data);                });        pageNum ++;    //总共有十个片段要追加，名称分别为1.html,2.html ...10.html        当当前页面的总数小于总数时，进行链接更新。        if(pageNum < 10){            $link.attr('href', './'+pageNum+'.html');                }        //当将所有片段追加完成后，移除链接。            else{                $link.remove();            }            }        })    });

以上的代码就可以进行动态的向页面追加数据了。

但是在谷歌的浏览器中会出现以下的错误：

jquery.js:8475 XMLHttpRequest cannot load file:///C:/Users/%E9%95%BF%E5%AD%99%E4%B8%B9%E5%87%A4/Desktop/webtest/1.html. Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, https.

在IE10的环境下进行测试的，没问题。
解决办法就是装一个web服务器，然后将文件拷到项目中，以web服务器中的路径访问，就没有问题啦！形如http://localhost:8080/ajax/ajaxLoad.html

由于还有鼠标悬浮事件，当我们将鼠标悬浮在某个图片上时，就会出现文字，移出时，图片上的文字消失。

$(document).ready(function(){        $('div .photo').hover(function(){            $(this).find('.details').fadeTo('slow', 0.7);        },function(){                $(this).find('.details').fadeOut('slow');        })    });或者可以将上面的代码组合起来减少冗余代码：$(document).ready(function(){    $('div.photo').on('mouseenter mouseleave',             function(event){            var $details = $(this).find('.details');            if(event.type == 'mouseenter'){                $details.fadeTo('slow', 0.7);                //0.7代表的是透明度            }            else{                $details.fadeOut('slow');            }        })});

当我们使用上面的两种代码为每个图片添加鼠标悬浮事件时，只有最初页面上的那些图片才会被绑定事件，而经过动态加载的图片上却没能绑定上事件。因为事件处理程序只会添加到调用方法时已经存在的元素上，像通过这种动态追加的元素，不会绑定那些事件。
所以有两种解决方案：
1. 在动态加载后重新绑定事件处理程序
2. 一开始就把事件绑定在存在的元素上，依赖于事件冒泡。

接下来就是使用jquery的委托方法;

$(document).ready(function(){        $('#gallery').on('mouseenter mouseleave', 'div.photo', function(event){            var $details = $(this).find('.details');            if(event.type == 'mouseenter'){                $details.fadeTo('slow', 0.7);            }            else{                $details.fadeOut('slow');            }        })    })

$(‘#gallery’).on(‘mouseenter mouseleave’, ‘div.photo’, function(event)中，在将’div.photo’作为第二个参数的情况下，.on()方法会把 this映射到 gallery中与该选择符匹配的元素。换句话说，就是this指向gallery中的 div class= ‘photo’的元素。

所以在最后追加的页面中，由于都属于gallery 下的元素，所以每一个图片都会加上相应的事件。
或许在你不知道要添加的页面属于哪个父级元素的话，可以将$(‘#gallery’).on( )中的’#gallery’替换成document。这样就不必担心选错容器。因为document是页面中所有元素的祖先。
但使用document有弊端：
当DOM嵌套结构很深，事件冒泡通过大量的祖先元素会有较大的性能损失。
但是还会有其他的原因让我们选择document作为委托作用域。
一般来说，只有当相应的DOM元素加载完毕，才会给它绑定事件处理程序。这就是为什么我们要把代码放到$(document).ready(function(){}内部的原因。可是document元素是随着页面加载几乎就立即可以调用的。把处理程序绑定到document不用等到完整的DOM构建结束。如上面的代码可以写为：‘

(function($){        $(document).on('mouseenter mouseleave', 'div.photo', function(event){            var $details = $(this).find('.details');            if(event.type == 'mouseenter'){                $details.fadeTo('slow', 0.7);            }            else{                $details.fadeOut('slow');            }        })    })(jQuery);

因为没有等到整个文档就绪，所以可以确保所有<div class= 'photo'>元素只要呈现在页面上，就可以应用mouseenter 和mouseleave行为。

上面就是关于利用jQuery动态追加页面数据以及事件委托的全部知识。下面附上源代码；

<!DOCTYPE html><html><head><meta charset = "utf-8" />    <title>动态加载</title>    <script type="text/javascript" src = "http://libs.baidu.com/jquery/1.9.0/jquery.js"></script>    <style type="text/css">    *{        margin: 0px;        padding: 0px;    }    #container{        position: relative;        width: 1300px;        margin: 0 auto;        /*background-color: #ccc;        height: auto;*/    }    #gallery{        position: relative;        width: 1300px;        margin: 0 auto;    }    .details{        display: none;    }    .photo{        padding: 20px;        border-radius: 5px;        border:1px solid #ccc;        box-shadow: 0 0 5px #ccc;        float: left;        margin: 8px;    }    .photo img{        /*z-index: 1;*/        width: 200px;        height: 300px;        clear: both;    }    .photo .details{        position: absolute;        z-index: 2;        padding-left: 20px;        margin-top:-200px;        /*clear: both;*/        overflow: hidden;    }    .description{        overflow: hidden;        width: 200px;        color: lightgreen;        font-size: 18px;        font-weight: bold;    }    .date{        font-size:16px;        margin: 20px 0px;        color: red;     }    .photographer{        font-size:14px;        font-family: "Arial" ;    }    .link a{        clear: both;        text-decoration: none;        padding-left: 90%;    }    h1{        text-align: center;     }    </style>    <script>    $(document).ready(function(){        var pageNum = 1;        $("#more-photos").click(function(event){            event.preventDefault();            var $link = $(this);            var url = $link.attr('href');            console.log(url);            if(url){                $.get(url, function(data){                    $("#gallery").append(data);                });                pageNum ++;                if(pageNum < 4){                    $link.attr('href', './'+pageNum+'.html');                }            else{                $link.remove();            }            }        })    })    // $(document).ready(function(){    //  $('div .photo').hover(function(){    //      $(this).find('.details').fadeTo('slow', 0.7);    //  },function(){    //          $(this).find('.details').fadeOut('slow');    //  })    // })    $(document).ready(function(){        $('#gallery').on('mouseenter mouseleave', 'div.photo', function(event){            var $details = $(this).find('.details');            if(event.type == 'mouseenter'){                $details.fadeTo('slow', 0.7);            }            else{                $details.fadeOut('slow');            }        })    })    </script></head><body><div id = "container"><h1> Photo Gallery</h1><div id = "gallery">    <div class = "photo">        <img src = "./images/1.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye ....</div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>    <div class = "photo">        <img src = "./images/2.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye.... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/3.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye.... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/4.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye .....</div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/5.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye ....</div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/6.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye ...</div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/7.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye.... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/8.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye..... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/9.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye ...... </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/10.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/11.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/12.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/13.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/14.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div>        <div class = "photo">        <img src = "./images/15.jpg">        <div class = "details">            <div class = "description">The Cullin Mountains, Isle of skye </div>            <div class = "date">12/24/2000</div>            <div class = "photographer"> Alasdair Dougall</div>        </div>    </div></div> <div class = "link"><a id = "more-photos" href = "1.html"> More Photos &gt;&gt;</a></div> </div></body></html>